Sintered diamond tool and method for manufacturing the same

ABSTRACT

A diamond sintered body tool ( 20 ) having superior adhesion resistance, chipping resistance and high strength includes a tool base material ( 22 ) including a diamond sintered body, and a surface layer ( 21 ) formed on a surface of the tool base material ( 22 ). The surface layer ( 21 ) includes at least one of silicon, a silicon oxide, a silicon carbide, a silicon nitride and a solid solution thereof. The tool base material ( 22 ) has an inner portion ( 22   b ) including a first content of an iron group metal, and a surface portion ( 22   a ) surrounding the inner portion ( 22   b  ) and including a second content of the iron group metal lower than the first content.

TECHNICAL FIELD

The present invention relates to diamond sintered body tools andmanufacturing methods thereof. More particularly, the present inventionrelates to a diamond sintered body tool having superior adhesionresistance, chipping resistance and strength as well as a manufacturingmethod thereof.

BACKGROUND ART

Since diamond sintered bodies have superior wear resistance andstrength, they are widely used as tool materials in a field thatrequires strength and wear resistance such as the fields of cuttingtools, drilling tools and wire drawn die tools. Such diamond sinteredbodies are known, for example, as the one provided by filling diamondpowder in a container made of a tungsten carbide—cobalt cemented carbideand sintering it at high temperature and under high pressure asdescribed in Japanese Patent Publication No. 52-12126. Furthermore,Japanese Patent Laying-Open No. 54-114513 describes a diamond sinteredbody obtained by previously mixing diamond powder and iron group metalpowder and maintaining the mixed powder at high temperature and underhigh pressure.

These diamond sintered bodies include an iron group metal such as cobaltas a sintering aid between sintered diamond particles.

As a diamond sintered body having improved heat resistance, the one inwhich an iron group metal is removed from the entire diamond sinteredbody is described in Japanese Patent Laying-Open Nos. 53-114589 and7-156003.

However, when a conventional diamond sintered body including an irongroup metal is used as a tool, cutting of a soft metal, especially analuminum alloy, results in adhesion of the workpiece material on thecutting edge of the tool depending on the cutting conditions and therebydeteriorates the roughness of the finished surface of the workpiecematerial as well as the processing precision.

In a diamond sintered body from which an iron group metal is removed,the diamond sintered body includes a gap and has smaller strength, andtherefore the diamond sintered body is easily chipped.

Therefore, the present invention was made to solve the above describedproblems, and its object is to provide a diamond sintered body toolcapable of suppressing adhesion of a soft metal such as an aluminumalloy and having superior strength and chipping resistance.

SUMMARY OF THE INVENTION

The inventors conducted a study of adhesion of a workpiece material onthe surface of a diamond sintered body tool when cutting an aluminumalloy. It was found out as a result that formation of a surface layerincluding at least one selected from silicon, a silicon oxide, a siliconcarbide, a silicon nitride and a solid solution thereof on the surfaceof the diamond sintered body tool is remarkably effective for preventingadhesion of a workpiece material, which led to the present invention.

In other words, on the rake face or the flank face of a tool which isengaged in cutting, the diamond sintered body as a tool base material isin contact with the aluminum alloy and, under low cutting rate or drycutting conditions, aluminum as a workpiece material adheres even on thesurface of chemically stable diamond. This would be because the bond ofaluminum and diamond on the surface of the diamond sintered body isrelatively strong.

In contrast, if a surface layer including at least one selected fromsilicon (Si), a silicon oxide (SiO₂), a silicon carbide (SiC), a siliconnitride (Si₃N₄) and a solid solution thereof is formed on the surface ofthe diamond sintered body tool, strongly bonded diamond and aluminum canbe prevented from being in contact with each other and aluminum can beprevented from being adhered on the rake surface or the flank face ofthe tool because any of these surface layers are weakly bonded toaluminum.

Especially when the surface layer is formed of Si, SiO₂, SiC or Si₃N₄,the bonding force of the surface layer and aluminum is lowered furthersince the surface layer is chemically stable, and the effect ofpreventing aluminum adhesion becomes higher.

The surface layer is generally formed in the following manner. When thesurface layer is made of silicon, silicon powder having a particle sizeof at least 1 μm and at most 20 μm, for example, is pressed against thetool surface to form a thin silicon adsorption layer on the surface.When the surface is made of a silicon oxide, a silicon carbide and/or asilicon nitride, the surface layer is formed at a temperature of 400° C.to 500° C. using an arbitrary material gas selected from SiH₄, O₂, N₂,C₂H₄ by the plasma CVD (Chemical Vapor Deposition) method, for example.Besides, the surface layer can also be formed by using similar materialgases and the methods such as the vacuum deposition, sputtering and ionplating.

Thus, in order to bring about the effect of adhesion prevention, thethickness of the surface layer formed on the diamond sintered body needsto be at least 0.1 nm. when the thickness of the surface layer exceeds 1μm, formation of the surface layer often makes the surface rougher,which, on the contrary, easily causes adhesion of a workpiece material.Therefore, the thickness of the surface layer formed on the diamondsintered body is preferably in the range from 0.1 nm to 1 μm.

When an iron group metal such as Fe, Co and Ni is used as a sinteringaid in the diamond sintered body, the iron group metal tends to be astarting point of adhesion caused at the cutting edge of the tool sincea good wetting property is observed between such iron group metals andaluminum. Although the “wettability” generally means easiness of contactbetween a solid and a liquid, it refers to easiness of close contactbetween a tool and a workpiece in this specification. Thus, “a badwettability” indicates a situation when a tool and a workpiece come intocontact, they do not closely contact each other. On the other hand, “agood wettability” indicates a situation when a tool and a workpiece comeinto contact, they tend to closely contact each other.

By previously removing an iron group metal included in the diamondsintered body from the surface and thereafter forming the surface layer,adhesion is effectively prevented even when the surface of the diamondsintered body is partially exposed by long term cutting.

In short, a diamond sintered body including an iron group metal is usedto manufacture a tool, and then the tool is immersed in an acid solutionto remove the iron group metal from the surface of the diamond sinteredbody. Then, a surface layer including at least one selected fromsilicon, a silicon oxide, a silicon carbide, a silicon nitride and asolid solution thereof is formed on the tool rake surface or the toolflank face of the diamond sintered body tool. Thus, adhesion resistancefor long term cutting can be improved.

Similarly, a diamond sintered body including an iron group metal isimmersed in an acid solution to remove the iron group metal from thesurface of the diamond sintered body. Thereafter, the diamond sinteredbody is used to form a tool. By forming a surface layer including atleast one selected from silicon, a silicon oxide, a silicon carbide, asilicon nitride and a solid solution thereof on the tool rake surface orthe tool flank face of the tool, adhesion resistance for long termcutting can be improved.

Furthermore, a diamond sintered body including an iron group metal isimmersed in an acid solution to remove the iron group metal from thesurface of the diamond sintered body. Thereafter, a surface layerincluding at least one selected from silicon, a silicon oxide, a siliconcarbide, a silicon nitride and a solid solution thereof is formed on thesurface of the diamond sintered body. By forming a tool using it,adhesion resistance for long term cutting can be improved.

Here, the diamond sintered body in which the iron group metal is removedfrom the surface as described above is characterized in that it includesan inner portion including a first content of the iron group metal, anda surface portion surrounding the inner portion and including a secondcontent of the iron group metal, the second content being lower than thefirst content. The sintered body structure is formed with such achanging content of the iron group metal because the cutting performanceof the sintered body is to be improved when it is used as a tool.

That is, when the iron group metal is removed over the entire sinteredbody, the diamond sintered body includes a gap and has small strengthand therefore the tool is easily chipped. In the present invention,since the iron group metal is removed only from the surface layer of thediamond sintered body, the strength of the sintered body is not loweredand the tool is not chipped. Therefore, adhesion resistance iseffectively improved.

In order to obtain such an effect, the second content of the iron groupmetal needs to be at most 2.0% by weight. when the thickness of asintered body surface portion having the second content is 2 nm or less,it is difficult to attain the effect of improving adhesion resistance byremoving the iron group metal from the surface of the diamond sinteredbody. When the thickness of a sintered body surface portion having thesecond content exceeds 5000 nm, the cutting edge of the tool is easilychipped. Therefore, the range of thickness of the surface portion havingthe second content is preferably at least 2 nm and at most 5000 nm fromthe surface of the diamond sintered body. Particularly, in a preferredembodiment of the present invention, the particle size of diamondparticles in the diamond sintered body is at least 0.1 μm and at most 60μm, and the content of sintered diamond particles in the diamondsintered body is at least 80% and at most 96% by volume.

The inventors conducted various studies of adhesion of a workpiecematerial on the surface of a diamond sintered body tool when cutting analuminum alloy. As a result, it was found out that adhesion of aworkpiece material starts from an iron group metal (iron, cobalt,nickel) included in the diamond sintered body tool.

Since the iron group metal (cobalt, iron, nickel) used as a sinteringcatalyst in the diamond sintered body has a good wettability withrespect to aluminum as a workpiece material, aluminum first comes intoclose contact with the iron group metal on the surface of the diamondsintered body tool. Thereafter, adhesion of aluminum spreads over theentire surface of the diamond sintered body tool as was found out.

Thus, in order to prevent adhesion, the iron group metal existing on thesurface of the diamond sintered body tool is removed, and therefore theadhesion resistance of the diamond sintered body tool is substantiallyimproved.

However, when the iron group metal is removed from the entire diamondsintered body as in conventional cases, a large number of gaps exist inthe diamond sintered body, which causes the strength to be lowered andchipping to occur easily. Then, the present invention aims to preventdecrease in the strength and occurrence of chipping by removing the irongroup metal only from the surface portion of the diamond sintered bodytool.

A diamond sintered body tool of the present invention based on such anidea includes a tool base material including a diamond sintered body,and a surface layer including at least one material selected from thegroup of silicon, a silicon oxide, a silicon carbide, a silicon nitrideand a solid solution thereof formed on a surface of the tool basematerial. The silicon oxide is preferably SiO₂. The silicon carbide ispreferably SiC. The silicon nitride is preferably Si₃N₄. The thicknessof the surface layer is preferably at least 0.1 nm and at most 1 μm. Thediamond sintered body tool is preferably brazed to a tool originalmaterial. The tool base material has a tool rake surface and a toolflank face, and the surface layer is preferably formed on at least oneof the tool rake surface and the tool flank face.

A diamond sintered body tool according to another aspect of the presentinvention includes a tool base material including a diamond sinteredbody, and a surface layer including at least one material selected fromthe group of silicon, a silicon oxide, a silicon carbide, a siliconnitride and a solid solution thereof formed on a surface of the toolbase material. The tool base material has an inner portion including afirst content of an iron group metal, and a surface portion surroundingthe inner portion and including a second content of the iron groupmetal, the second content being lower than the first content. Thesilicon oxide is preferably SiO₂. The silicon carbide is preferably SiC.The silicon nitride is preferably Si₃N₄. The thickness of the surfacelayer is preferably at least 0.1 nm and at most 1 μm. The second contentis preferably at most 2.0% by weight. A portion which is at least 2 nmand at most 5000 nm in depth from the diamond sintered body surface ispreferably the surface portion. The diamond sintered body tool ispreferably brazed to the tool original material. Preferably, the toolbase material has a tool rake surface or a tool flank face, and thesurface layer is formed on at least one of the tool rake surface and thetool flank face.

A diamond sintered body tool according to another aspect of the presentinvention includes an inner portion including a first content of an irongroup metal, and a surface portion surrounding the inner portion andincluding a second content of the iron group metal, the second contentbeing lower than the first content.

According to such a structure, the content of the iron group metal islow in the surface portion, and it becomes difficult for aluminum to beadhered on the surface portion. Since a larger amount of iron groupmetal exists in the inner portion than in the surface portion,occurrence of a gap in the inner portion can be suppressed. Therefore,the strength and the chipping resistance are not lowered.

The second content is preferably at most 2.0% by weight.

A portion which is at least 2 nm and at most 5000 nm in depth from thediamond sintered body tool surface is preferably the surface portion.

For a sintered body having a relatively lower diamond content in whichthe content of sintered diamond particles is at most 96% by volume, orfor a sintered body in which the diameter of a sintered diamond particleis at most 60 μm, adhesion of aluminum is particularly easily caused.Since the minimum size of an actually producible sintered diamondparticle is 0.1 μm and the diamond content in this case is 80% byvolume, the effects of the present invention are particularly evidentfor a diamond sintered body tool in which the size of a diamond particleis at least 0.1 μm and at most 60 μm or the content of sintered diamondparticles is at least 80% and at most 96% by volume.

The diamond sintered body tool is preferably brazed to a tool originalmaterial.

Furthermore, at least one of the tool rake surface and the tool flankface is preferably formed on the surface portion.

Adhesion of the above described workpiece made of an aluminum alloy isalso greatly influenced by cutting conditions.

Especially in the case the cutting speed is under 200 m/min, adhesioneasily occurs on the surface of the diamond sintered body tool.Therefore, for milling or drilling tools of which the cutting speed islower, such as a reamer tool, an end mill tool, a drill tool and aboring tool, the present invention provides remarkable effects foradhesion resistance.

A method of manufacturing a diamond sintered body tool according to oneaspect of the present invention includes the steps of (1) preparing adiamond sintered body, (2) processing the diamond sintered body to forma diamond sintered body tool, and (3) forming a surface layer includingat least one selected from the group of silicon, a silicon oxide, asilicon carbide, a silicon nitride and a solid solution thereof on asurface of the diamond sintered body tool.

A method of manufacturing a diamond sintered body tool according toanother aspect of the present invention includes the steps of (1)preparing a diamond sintered body including an iron group metal, (2)processing the diamond sintered body to form a diamond sintered bodytool, and (3) surface treating the diamond sintered body tool byimmersing the diamond sintered body tool in an acid solution to removethe iron group metal from a surface portion and thereby make the contentof the iron group metal lower in the surface portion than in the innerportion.

The acid solution preferably includes at least one selected from thegroup of nitric acid, hydrochloric acid and hydrofluoric acid.

The content of iron group metal in the surface portion is preferably atmost 2.0% by weight.

A method of manufacturing a diamond sintered body tool according tostill another aspect of the present invention includes the steps of (1)preparing a diamond sintered body including an iron group metal, (2)surface treating the diamond sintered body by immersing the diamondsintered body in an acid solution to remove the iron group metal from asurface portion of the diamond sintered body and thereby make thecontent of the iron group metal lower in the surface portion than in aninner portion of the diamond sintered body, and (3) processing thesurface treated diamond sintered body to obtain a diamond sintered bodytool.

In these methods of manufacturing a diamond sintered body, the contentof the iron group metal is made lower in the surface portion than in theinner portion, and therefore a diamond sintered body tool havingsuperior adhesion resistance, strength and chipping resistance can beobtained.

A method of manufacturing a diamond sintered body tool according to afurther aspect of the present invention includes the steps of (1)preparing a diamond sintered body including an iron group metal, (2)processing the diamond sintered body to form a diamond sintered bodytool, (3) immersing the diamond sintered body tool in an acid solutionto remove the iron group metal from a surface portion and thereby makethe content of the iron group metal lower in the surface portion than inan inner portion, and (4) forming a surface layer including at least oneselected from the group of silicon, a silicon oxide, a silicon carbide,a silicon nitride and a solid solution thereof on a tool rake surface ora tool flank face of the diamond sintered body tool.

The acid solution preferably includes at least one selected from thegroup of nitric acid, hydrochloric acid and hydrofluoric acid.

The content of the iron group metal in the surface portion is preferablyat most 2.0% by weight.

A method of manufacturing a diamond sintered body tool according to afurther aspect of the present invention includes the steps of (1)preparing a diamond sintered body including an iron group metal, (2)immersing the diamond sintered body in an acid solution to remove theiron group metal from a surface portion of the diamond sintered body andthereby make the content of the iron group metal lower in the surfaceportion than in an inner portion, (3) processing the surface treateddiamond sintered body to obtain a diamond sintered body tool, and (4)forming a surface layer including at least one selected from the groupof silicon, a silicon oxide, a silicon carbide, a silicon nitride and asolid solution thereof on a surface of the surface treated diamondsintered body tool.

The acid solution preferably includes at least one selected from thegroup of nitric acid, hydrochloric acid and hydrofluoric acid.

The content of the iron group metal in the surface portion is preferably2.0% by weight.

A method of manufacturing a diamond sintered body tool according to afurther aspect of the present invention includes the steps of (1)preparing a diamond sintered body including an iron group metal, (2)immersing the diamond sintered body in an acid solution to remove theiron group metal from a surface portion of the diamond sintered body andthereby make the content of the iron group metal lower in the surfaceportion than in an inner portion of the diamond sintered body tool, and(3) forming a surface including at least one selected from the group ofsilicon, a silicon oxide, a silicon carbide, a silicon nitride and asolid solution thereof on a surface of the surface treated diamondsintered body, and (4) processing the diamond sintered body on which thesurface layer is formed to obtain a diamond sintered body tool.

The acid solution preferably includes at least one selected from thegroup of nitric acid, hydrochloric acid and hydrofluoric acid.

The content of the iron group metal in the surface portion is preferablyat most 2.0% by weight.

A method of manufacturing a diamond sintered body tool according to afurther aspect of the present invention includes the steps of (1)preparing a diamond sintered body, (2) forming a surface layer includingat least one selected from the group of silicon, a silicon oxide, asilicon carbide, a silicon nitride and a solid solution thereof on asurface of the diamond sintered body, and (3) processing the diamondsintered body on which the surface layer is formed to form a diamondsintered body tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a diamond sintered body toolaccording to one aspect of the present invention.

FIG. 2 is a schematic sectional view of a diamond sintered body toolaccording to another aspect of the present invention.

FIG. 3 is a schematic sectional view of a diamond sintered body toolaccording to a further aspect of the present invention.

DETAILED DESCRIPTION OF BEST MODES FOR CARRYING OUT THE INVENTION

In the following, best modes for carrying out the present invention willbe described with reference to the figures.

FIG. 1 is a schematic sectional view of a diamond sintered body toolaccording to one aspect of the present invention. Referring to FIG. 1, adiamond sintered body tool 10 includes a tool base material 12 includinga diamond sintered body, and a surface layer 11 formed on a surface oftool base material 12. Surface layer 11 includes at least one selectedfrom silicon, a silicon oxide, a silicon carbide, a silicon nitride anda solid solution thereof.

FIG. 2 is a schematic sectional view of a diamond sintered body toolaccording to another aspect of the present invention. Referring to FIG.2, a diamond sintered body tool 20 includes a tool base material 22including a diamond sintered body, and a surface layer 21 formed on asurface of tool base material 22. Surface layer 21 includes at least oneselected from silicon, a silicon oxide, a silicon carbide, a siliconnitride and a solid solution thereof. Tool base material 22 has an innerportion 22 b including a first content of an iron group metal, and asurface portion 22 a surrounding inner portion 22 b and including asecond content of the iron group metal, the second content being lowerthan the first content.

FIG. 3 is a schematic sectional view of a diamond sintered body toolaccording to a further aspect of the present invention. Referring toFIG. 3, a diamond sintered body tool 30 has an inner portion 32 bincluding a first content of an iron group metal, and a surface portion32 a surrounding inner portion 32 b and including a second content ofthe iron group metal, the second content being lower than the firstcontent, and includes a tool base material 32 having a diamond sinteredbody.

FIRST EMBODIMENT

Diamond particles having a diameter size in the range from 0.1 to 4 μmwere first prepared. A sintering aid made of iron group metal (cobalt,iron and nickel) particles was also prepared. The diamond particles andthe iron group metal were mixed by a ball mill so that the diamondcontent was 90% by volume, and the mixed powder was formed. After themixed powder was heated in vacuum at a temperature of 800° C. for onehour, it was filled in a capsule made of a cemented carbide andmaintained and sintered for one hour under the condition that thepressure was 50,000 atmospheric pressure and the temperature was 1,400°C. Thus, such a diamond sintered body was obtained that had a sintereddiamond particle size of 0.1 to 4 μm and an iron group metal content of15% by weight.

The similar process was repeated to obtain five diamond sintered bodieshaving the same composition. Each of these five diamond sintered bodieswas processed to the shape of a reamer tool having two cutting edges.

These reamer tools were immersed in an acid solution (aqua regia) fortime periods indicated in Table 1 to remove the iron group metal fromsurface portions of the reamer tools and thereby obtain Samples No. 1 to5. For Samples No. 1 to 5, the depth of a portion having an iron groupcontent of at most 2.0% by weight was examined. The results are as shownin Table 1.

TABLE 1 Time for immersion Depth of a portion in an acid having an irongroup Sample solution metal content of at most No. (min.) 2.0% by weight(nm) Comparative example 1 0 0 Comparative example 2 0.5 1.5 Example ofthe 3 5 2.5 invention Example of the 4 60 4000 invention Comparativeexample 5 180 6000

Then, Samples No. 1 to 5 were used to process a workpiece under thefollowing cutting conditions.

workpiece: an aluminum alloy (JIS A6061, T6 process material)

processed hole diameter: 15 mm

cutting speed: 100 m/min

feed rate: 0.1 mm/rev

coolant: wet condition

It was examined whether the cutting processing caused adhesion on atleast one of the rake surface and the flank face of a reamer tool. Theroughness (R_(max)) of a finished surface of the workpiece was alsochecked. The results are as shown in Table 2.

TABLE 2 Roughness of a Sample Existence of finished No. adhesion surfaceR_(max) (μm) Comparative 1 with adhesion 9.2 example Comparative 2 withadhesion 8.6 example Example of the 3 without adhesion 1.2 inventionExample of the 4 without adhesion 1.1 invention Comparative 5 chippedcutting edge — example

It was found out from Table 2 that, for each of Samples No. 3 and 4, aportion including a small amount of the iron group metal had a suitabledepth, and therefore the aluminum alloy was not adhered and superiorroughness of a finished surface was obtained. On the contrary, forSample No. 1 in which a large amount of the iron group metal existed onthe surface, or for Sample No. 2 in which a portion having a smallamount of the iron group metal was shallow, the aluminum alloy wasadhered on the rake surface and the resulting deterioration of theroughness of a finished surface was observed. For Sample No. 5, aportion having a small amount of the iron group metal existed deeper,and therefore a portion having a pore became larger, the cutting edge ofthe tool was chipped, and found not to continue to cut.

SECOND EMBODIMENT

Diamond particles having particle sizes shown in Table 3 were firstprepared. These diamond particles and an iron group metal were mixed,and heated and sintered similarly to the first embodiment to obtaindiamond sintered bodies (Samples No. 11 to 18). For each sample, thediameter of a sintered diamond particle was measured. As a result, thediameter of the sintered diamond particle was equal to the diameter ofthe pre-sintered diamond particle. The diamond content and the irongroup metal content were also measured. The results are as shown inTable 3.

TABLE 3 Diameter of a Diamond Iron group Sample diamond content metalcontent No. particle (μm) (% by volume) (% by weight) 11 0.5 85 17 12 590 15 13 25 95 12 14 70 98  6 15 0.5 85 17 16 5 90 15 17 25 95 12 18 7098  6

Then, each of Samples No. 11 to 14 was immersed in an hydrochloric acidsolution of 60% by weight to remove the iron group metal from a surfaceportion of the diamond sintered body. For each sample, the depth of aportion having an iron group metal content of at most 2.0% by weight wasmeasured. The results are as shown in Table 4.

TABLE 4 Depth of a portion having an Sample iron group metal content No.of at most 2.0% by weight (nm) 11 30 12 30 13 30 14 30 15 — 16 — 17 — 18—

Then, each of the diamond sintered bodies denoted by Samples No. 11 to18 was processed to the shape of the cutting edge of a drill. At thistime, for each of Samples No. 11 to 14, a portion which was 25 nm indepth from the rake surface and the flank face had an iron group metalcontent of at most 2.0% by weight. The drill cutting edges were brazedto drill tool original materials made of a cemented carbide tomanufacture drill tools. The drill tools were used for drilling underthe following conditions.

workpiece: an aluminum alloy (JIS ADC12, T6 process material)

drilling diameter: 5 mm

cutting speed: 50 m/min

feed rate: 0.08 mm/tooth

coolant: wet condition

After the drilling processing, it was examined whether the aluminumalloy was adhered on the cutting edge of a drill. The diameter of theprocessed hole was also measured. The results are as shown in Table 5.

TABLE 5 Sample Existence Diameter of a No. of adhesion processed hole(mm) Examples of the 11 without adhesion 5.002 invention 12 withoutadhesion 4.998 13 without adhesion 5.001 14 without adhesion 5.000Comparative 15 with significant 5.044 examples adhesion 16 withsignificant 5.021 17 adhesion with significant 5.015 adhesion 18 slightadhesion 5.006

It was found out from Table 5 that, for each of Samples No. 11 to 14 inwhich the iron group metal content of the surface portion was small, thealuminum alloy was not adhered. Since the tolerance of a processed hole,that is, the range permissible as an error is 5±0.006 mm, it can be seenthat the processed holes formed in Samples No. 11 to 14 are within thetolerance.

On the contrary, for each of Samples No. 15 to 17, the iron group metalwas not removed from the surface of a cutting edge, that is, a largeamount of the iron group metal existed on the surface of the cuttingedge, and therefore the aluminum was adhered and it was difficult toobtain a processed hole diameter within the tolerance. For Sample No.18, the diameter of a diamond particle was large although the iron groupmetal existed on the surface of a cutting edge, and therefore adhesionwas slight. It was therefore difficult to obtain a processed holediameter within the tolerance. It was made clear from these results thatapplication of the present invention is effective for preventingadhesion particularly in a sintered body in which the diameter of asintered diamond particle is small and the diamond content is low.

THIRD EMBODIMENT

TABLE 6 Thickness of a Sample Composition of surface layer No. a surfacelayer (nm) 21 silicone layer 5 (framework of molecular structure:—Si—O—Si—O—) 22 Si 5 23 SiO₂ 5 24 SiC 5 25 Si₃N₄ 5 26 without anysurface layer —

Table 6 shows examples of various diamond sintered tools prepared toexamine the influences that mainly the surface composition exerts on theadhesion resistance of a diamond sintered body tool. In short, for anytools of Table 6, a diamond sintered body tool having a particle size ofat least 0.1 μm and at most 4 μm was used as a tool base material.Surface layers of various compositions were formed on the rake surfacesand the flank faces of the diamond sintered body tools.

Each of the tools denoted by Samples No. 21 to 26 was first manufacturedto an insert of a desired shape having a cutting edge made of a diamondsintered body.

Thereafter, for Sample No. 21, silicone grease was applied to the toolrake surface and the tool flank face of the diamond sintered body toform a silicone layer having the thickness indicated in Table 6 based onthe molecular structure of a siloxane bond (—Si—O—Si—O—) shown in Table6.

For the tool denoted by Sample No. 22, the silicon layer having thethickness indicated in Table 6 was formed by pressing silicon powderagainst the portions of the tool rake surface and the tool flank face ofthe diamond sintered body.

For the tools denoted by Samples No. 23 to 25, the surface layers havingthe compositions indicated in Table 6 were formed at a composingtemperature of at least 400° C. and at most 500° C. by the plasma CVDmethod employing a gas selected from SiH₄, O₂ and C₂H₄, respectively.

For comparison, the tool denoted by Sample No. 26 was not processed toform a surface layer.

By performing the cutting processing using the tools under the followingconditions, the adhesion resistance of each tool was evaluated.

workpiece: an aluminum alloy (JIS A6061, T6 process material)

cutting speed: 60 m/min

depth of cut: 0.3 mm

feed rate: 0.1 mm/rev

coolant: dry condition

The results are shown in Table 7.

TABLE 7 Sample Existence Roughness of a finished No. of adhesion surfaceRmax (μm) 21 without adhesion 3.8 22 without adhesion 4.1 23 withoutadhesion 3.9 24 without adhesion 4.0 25 without adhesion 4.1 26 withadhesion 12.3

As a result of the above test, superior results were attained whenSamples No. 21 to 25 as sintered body tools of the present inventionwere used for processing. It was made clear that since a surface layerhaving a weak bonding force with aluminum existed on the tool rakesurface and the tool flank face of the diamond sintered body tool,aluminum was not adhered and superior roughness of the finished surfacewas obtained. On the contrary, for Sample No. 26 which is a tool nothaving a special surface layer, the aluminum alloy was adhered on thetool rake surface and the resulting deterioration of the roughness ofthe finished surface was observed.

FOURTH EMBODIMENT

TABLE 8 Roughness of a Sample Composition of Thickness of a surfacelayer No. a surface layer surface layer (nm) (μm) 31 SiO₂   5 0.013 32SiO₂  200 0.022 33 SiO₂ 1000 0.055 34 SiO₂ 1800 0.105 35 without any —0.010 surface layer

Table 8 shows examples of various diamond tools prepared to examine theinfluences mainly the surface layer thickness exerts on the adhesionresistance of a diamond sintered body tool. In short, for the tools inTable 8, diamond sintered body tools each having a particle size of atleast 4 μm and at most 10 μm were used as tool base materials. Surfacelayers of various thickness values were formed on the rake surfaces ofthe diamond sintered body tools.

For each of the tools denoted by Samples No. 31 to 34, an SiO₂ layerhaving the thickness indicated in Table 8 was formed on a lapped diamondsintered body surface by the ion plating method. Thereafter, thesintered body was brazed to a reamer shank made of a cemented carbide tomanufacture a diamond sintered body reamer tool having a desired shape.

For comparison, a diamond sintered body tool not having any surfacelayer was used to manufacture a tool by a similar method to that forproducing Samples No. 31 to 34, and thus the tool denoted by Sample No.35 was obtained. By performing the cutting processing using these toolsunder the following conditions, the adhesion resistance of each tool wasevaluated.

workpiece: an aluminum alloy (JIS ADC12, T6 process material)

processed hole diameter: 15 mm

cutting speed: 100 m/min

feed rate: 0.1 mm/tooth

coolant: wet condition

The results are as shown in Table 9.

TABLE 9 Sample Existence Roughness of a finished No. of adhesion surfaceRmax (μm) 31 without adhesion 1.0 32 without adhesion 1.2 33 withoutadhesion 1.1 34 slight adhesion 2.1 35 with adhesion 9.3

When Samples No. 31 to 33 as sintered body tools of the presentinvention were used for processing, a surface layer having a weakbonding force with aluminum existed on the rake surface of the diamondsintered body tool, and therefore the aluminum alloy was not adhered. Itwas therefore made clear that superior roughness of the finished surfacewas obtained.

On the contrary, for the tool denoted by Sample No. 34 having a thicksurface layer, the thick surface layer deteriorated the roughness of thetool rake surface as shown in Table 9, and therefore the aluminum alloywas slightly adhered. It was also found out in this sample that theroughness of the finished surface was slightly deteriorated although notremarkable.

However, for the sample denoted by Sample No. 35 not having any specialsurface layer, diamond on the rake surface and aluminum bonded eachother strongly, the workpiece material was adhered, and the resultingdeterioration of the roughness of the finished surface was recognized.

FIFTH EMBODIMENT

TABLE 10 Sam- Time of immersion Depth of a portion having an Thicknessof ple in an acid solution iron group metal content of a surface No.(min.) at most 2.0% by weight (nm) layer (nm) 41  5 2.5 3 42  60 4000 343 180 6000 3 44 without immersion 0 3 45 without immersion 0 0

Table 10 shows various diamond sintered body tools prepared to examinethe influences the depth of a portion from which an iron group metal wasremoved before forming a surface layer exerts on the adhesion resistanceof a diamond sintered body tool in the diamond sintered body toolemploying the iron group metal as a sintering catalyst. In short, foreach of the tools in Table 10, a diamond sintered body having particlesin the particle size range of at least 2 μm and at most 8 μm andemploying cobalt as a main sintering catalyst were used as a tool basematerial. Before a surface layer was formed on the tool rake surface,the depth of a portion having an iron group metal content of at most2.0% by weight (portion substantially not including the iron groupmetal) was variously set.

For each of the tools denoted by Samples No. 41 to 43, the tool was adesired reamer tool having two cutting edges, and the tool was immersedin a nitric acid solution at normal temperature to dissolve and extractcobalt from the rake surface and the flank face of the diamond sinteredbody tool.

The time for immersing the tools in the nitric acid solution was 5, 60and 180 minutes, respectively. As a result, the depth of each of theportions having an iron group metal content of at most 2.0% by weightwas as shown in Table 10. Thereafter, a similar method to that of thethird embodiment was used to apply silicone grease on the rake surfaceand the flank face of each of the tools denoted by Samples No. 41 to 43,and thus surface layers including silicone and having a thickness of 3nm were formed on the diamond sintered body surfaces.

For comparison, Samples No. 44 and 45 were manufactured. Sample No. 44was a tool which was manufactured by a similar method to Samples No. 41to 43 except that a surface layer was formed on the surface of a diamondsintered body without immersion in an acid solution. Sample No. 45 was atool which was manufactured by a similar method to Samples No. 41 to 43except that immersion in an acid solution and formation of a surfacelayer were not conducted. By performing the cutting processing usingthese tools, adhesion was evaluated.

workpiece: an aluminum alloy (JIS A6061, T6 process material)

processed hole diameter: 20 mm

cutting speed: 80 m/min

feed rate: 0.15 mm/tooth

coolant: dry condition

The results are as shown in Table 11.

TABLE 11 Roughness of a Sample Existence finished surface No. ofadhesion Rmax (μm) 41 without adhesion 1.3 42 without adhesion 1.1 43without adhesion 1.2 (in some case, the cutting edge is chipped) 44slight adhesion 1.6 45 with adhesion 13.9

As a result, when Samples No. 41 to 44 as sintered body tools of thepresent invention were used for processing, a surface layer having aweak bonding force with aluminum existed on the rake surface of adiamond sintered body tool, and therefore the aluminum alloy was notadhered. Therefore, it was made clear that superior roughness of thefinished surface was obtained.

Above all, for Samples No. 41 and 42 in which the surface layer wasformed after removing an iron group metal from the surface of thediamond sintered body tool, it was recognized that the workpiecematerial was not adhered even for long term cutting and remarkableeffects were attained.

Similarly, for the tool denoted by Sample No. 43 in which the surfacelayer was formed after removing an iron group metal, it was observedthat although adhesion was not caused, the thickness of a portion fromwhich the iron group metal was removed was large and the strength of thecutting edge is low, and therefore the cutting edge was chipped in somecases.

For the tool denoted by Sample No. 45 in which surface treatment was notprovided, substantial adhesion was recognized.

SIXTH EMBODIMENT

TABLE 12 Sam- Concentration of Iron group metal ple hydrochloric acidcontent Existence of an SiC No. (% by volume) (% by weight) surfacelayer 51 10 2.0 with a surface layer 52 30 1.1 with a surface layer 5360 0.6 with a surface layer 54 — 5.0 with a surface layer 55 — 5.0without a surface layer

Table 12 shows examples of various drill tools prepared to examine theinfluences that the iron group metal content of a previouslyacid-treated diamond sintered body exerts on adhesion.

In short, for each of the tools denoted by Samples No. 51 to 53 in Table12, a diamond sintered body tool base material was first immersed in ahydrochloric acid solution to dissolve and extract an iron group metal.At this time, the content of the iron group metal in the diamondsintered body surface portion was adjusted to the content shown in Table12 by changing the concentration of hydrochloric acid. Thereafter, eachtool base material was brazed to a drill tool original material made ofa cemented carbide to form the shape of a cutting edge. Thereafter, asimilar method to that of the third embodiment was used to form asurface layer having a thickness of 3 nm and made of SiC on the toolrake surface and the tool flank face of the diamond sintered drill.

For comparison, the drill tool denoted by Sample No. 54 was prepared.Although Sample No. 54 was manufactured by a similar method to SamplesNo. 51 to 53, each diamond tool base material was not immersed in anacid solution to manufacture the tool, and then a surface layer having athickness of 3 nm and made of SiC was formed on the tool rake surfaceand the tool flank face. For the drill tool denoted by Sample No. 55,the tool was formed without immersion in an acid solution and formationof a surface layer.

By performing the cutting processing using them under the followingconditions, adhesion was evaluated.

workpiece: an aluminum alloy (JIS ADC12, T6 process material)

processed hole diameter: 5 mm

cutting speed: 50 m/min

feed rate: 0.08 mm/rev

coolant: wet condition

The results are as shown in Table 13.

TABLE 13 Sample Existence Diameter of a processed hole No. of adhesion(tolerance φ5 ± 0.006 mm) 51 without adhesion 5.002 52 without adhesion4.998 53 without adhesion 5.001 54 slight adhesion 5.006 55 significantadhesion 5.044

It was made clear that when Samples No. 51 to 54 as sintered body toolsof the present invention were used for processing, the aluminum alloywas not adhered and processed hole diameters within the tolerance wereobtained. Especially for each of the tools denoted by Samples No. 51 to53, it was recognized that even if the surface layer is worn duringprocessing and the diamond sintered body surface is partially exposed,the effect of adhesion prevention is provided for a long period becausean iron group metal which tends to be a starting point of adhesion doesnot exist on the exposed diamond sintered body surface.

It was recognized that similar effects are attained even when a diamondsintered body tool is manufactured by forming a surface layer on thesurface of a diamond sintered body base material after the diamondsintered body tool base material is acid-treated, and thereafterperforming brazing and provision of a cutting edge.

As described above, the diamond sintered body tool according to thepresent invention is useful for the field which requires strength andwear resistance such as a cutting edge tool, or a drilling edge tool.

What is claimed is:
 1. A diamond sintered body tool (10) that issuitable and adapted to be used for cutting an aluminum alloy,comprising: a tool base material (12) including a diamond sintered body;and a surface layer (11) having a thickness of at least 0.1 nm and lessthan 1 μm and including at least one material selected from the group ofsilicon, a silicon oxide, a silicon carbide, a silicon nitride and asolid solution thereof, formed on a surface of said tool base material(12).
 2. The diamond sintered body tool according to claim 1, whereinsaid surface layer consists essentially of said silicon oxide which isSiO₂.
 3. The diamond sintered body tool according to claim 1, whereinsaid surface layer consists essentially of said silicon carbide which isSiC.
 4. The diamond sintered body tool according to claim 1, whereinsaid surface layer consists essentially of said silicon nitride which isSi₃N₄.
 5. The diamond sintered body tool according to claim 1, furthercomprising a tool original material and a braze layer interposed betweenand securing said tool base material to said tool original material. 6.The diamond sintered body tool according to claim 1, wherein said toolbase material has a tool rake surface or a tool flank face, and saidsurface layer is formed on at least one of said tool rake surface andsaid tool flank face.
 7. The diamond sintered body tool according toclaim 1, wherein said thickness of said surface layer is at least 3 nmand not more than 200 nm.
 8. The diamond sintered body tool according toclaim 1, wherein said material is said silicon, and said surface layeressentially consists of said silicon.
 9. The diamond sintered body toolaccording to claim 1, wherein said surface layer consists of a materialincluding silicon and oxygen forming a siloxane bond.
 10. A diamondsintered body tool (20) that is suitable and adapted to be used forcutting an aluminum alloy, comprising: a tool base material (22)including a diamond sintered body; and a surface layer (21) having athickness of at least 0.1 nm and less than 1 μm and including at leastone material selected from the group of silicon, a silicon oxide, asilicon carbide, a silicon nitride and a solid solution thereof formedon a surface of the tool base material (22), wherein said diamondsintered body of said tool base material (22) has an inner portion (22b) including a first content of an iron group metal, and a surfaceportion (22 a) extending at least 2 nm and at most 5000 nm in depth fromsaid surface of said diamond sintered body, surrounding said innerportion (22 b), and including a second content of said iron group metal,said second content being lower than said first content.
 11. The diamondsintered body tool according to claim 10, wherein said surface layerconsists essentially of said silicon oxide which is SiO₂.
 12. Thediamond sintered body tool according to claim 10, wherein said surfacelayer consists essentially of said silicone carbide which is SiC. 13.The diamond sintered body tool according to claim 10, wherein saidsurface layer consists essentially of said silicon nitride which isSi₃N₄.
 14. The diamond sintered body tool according to claim 10, whereinsaid second content is at most 2.0% by weight.
 15. The diamond sinteredbody tool according to claim 10, further comprising a tool originalmaterial and a braze layer interposed between and securing said toolbase material to said tool original material.
 16. The diamond sinteredbody tool according to claim 10, wherein said tool base material has atool rake surface or a tool flank face, and said surface layer is formedon at least one of said tool rake surface and said tool flank face. 17.The diamond sintered body tool according to claim 10, wherein saidthickness of said surface layer is at least 3 nm and not more than 200nm.
 18. The diamond sintered body tool according to claim 10, whereinsaid material is said silicon, and said surface layer essentiallyconsists of said silicon.
 19. The diamond sintered body tool accordingto claim 10, wherein said surface layer consists of a material includingsilicon and oxygen forming a siloxane bond.
 20. A diamond sintered bodytool that is suitable and adapted to be used for cutting an aluminumalloy, comprising a diamond sintered body that comprises: an innerportion (32 b) including a first content of an iron group metal; and asurface portion (32 a) extending at least 2 nm and at most 5000 nm indepth from a surface of said diamond sintered body, surrounding saidinner portion (32 b), and including a second content of said iron groupmetal, said second content being lower than said first content.
 21. Thediamond sintered body tool according to claim 20, wherein said secondcontent is at most 2.0% by weight.
 22. The diamond sintered body toolaccording to claim 20, further comprising a tool original material and abraze layer interposed between and securing said diamond sintered bodyto said tool original material.
 23. The diamond sintered body toolaccording to claim 20, wherein at least one of a tool rake surface and atool flank face is formed on said surface portion.
 24. A method ofmanufacturing a diamond sintered body tool that is suitable and adaptedto be used for cutting an aluminum alloy, comprising the steps of:preparing a diamond sintered body; processing said diamond sintered bodyto form a diamond sintered body tool; and forming a surface layer havinga thickness of at least 0.1 nm and less than 1 μm and including at leastone material selected from the group of silicon, a silicon oxide, asilicon carbide, a silicon nitride and a solid solution thereof on asurface of said diamond sintered body tool.
 25. A method ofmanufacturing a diamond sintered body tool that is suitable and adaptedto be used for cutting an aluminum alloy, comprising the steps of:preparing a diamond sintered body including an iron group metal;processing said diamond sintered body to form a diamond sintered bodytool; and surface treating said diamond sintered body tool by immersingsaid diamond sintered body tool in an acid solution to remove at leastsome of said iron group metal from a surface portion of said diamondsintered body extending at least 2 nm and at most 5000 nm in depth froma surface of said diamond sintered body and thereby to make a content ofsaid iron group metal lower in said surface portion than in an innerportion of said diamond sintered body.
 26. The method of manufacturing adiamond sintered body tool according to claim 25, wherein said acidsolution includes at least one selected from the group of nitric acid,hydrochloric acid and hydrofluoric acid.
 27. The method of manufacturinga diamond sintered body tool according to claim 25, wherein the contentof said iron group metal in said surface portion is at most 2.0% byweight.
 28. A method of manufacturing a diamond sintered body tool thatis suitable and adapted to be used for cutting an aluminum alloycomprising the steps of: preparing a diamond sintered body including aniron group metal; processing said diamond sintered body to form adiamond sintered body tool; immersing said diamond sintered body tool inan acid solution to remove at least some of the iron group metal from asurface portion of said diamond sintered body extending at least 2 nmand at most 5000 nm in depth from a surface of said diamond sinteredbody and thereby to make a content of said iron group metal lower insaid surface portion than in an inner portion of said diamond sinteredbody; and forming a surface layer having a thickness of at least 0.1 nmand less than 1 μm and including at least one material selected from thegroup of silicon, a silicon oxide, a silicon carbide, a silicon nitrideand a solid solution thereof on said surface of the diamond sinteredbody tool.
 29. The method of manufacturing a diamond sintered body toolaccording to claim 28, wherein said acid solution includes at least oneselected from nitric acid, hydrochloric acid and hydrofluoric acid. 30.The method of manufacturing a diamond sintered body tool according toclaim 28, wherein the content of said iron group metal in said surfaceportion is at most 2.0% by weight.
 31. A method of manufacturing adiamond sintered body tool that is suitable and adapted to be used forcutting an aluminum alloy, comprising the steps of: preparing a diamondsintered body including an iron group metal; immersing said diamondsintered body in an acid solution to remove at least some of said irongroup metal from a surface portion of said diamond sintered bodyextending at least 2 nm and at most 5000 nm in depth from a surface ofsaid diamond sintered body and thereby to make a content of said irongroup metal lower in said surface portion than in an inner portion ofsaid diamond sintered body; after said immersing step, processing saiddiamond sintered body to obtain a diamond sintered body tool; and aftersaid processing step, forming a surface layer having a thickness of atleast 0.1 μm and less than 1 μm and including at least one materialselected from the group of silicon, a silicon oxide, a silicon carbide,a silicon nitride and a solid solution thereof on said surface of saiddiamond sintered body.
 32. The method of manufacturing a diamondsintered body tool according to claim 31, wherein said acid solutionincludes at least one selected from the group of nitric acid,hydrochloric acid and hydrofluoric acid.
 33. The method of manufacturinga diamond sintered body tool according to claim 31, wherein the contentof said iron group metal in said surface portion is at most 2.0% byweight.
 34. A method of manufacturing a diamond sintered body tool thatis suitable and adapted to be used for cutting an aluminum alloy,comprising the steps of: preparing a diamond sintered body including aniron group metal; immersing said diamond sintered body in an acidsolution to remove at least some of said iron group metal from a surfaceportion of said diamond sintered body extending at least 2 nm and atmost 5000 nm in depth from a surface of said diamond sintered body andthereby to make a content of said iron group metal lower in said surfaceportion than in an inner portion of said diamond sintered body; aftersaid immersing step, forming a surface layer having a thickness of atleast 0.1 nm and less than 1 μm and including at least one materialselected from the group of silicon, a silicon oxide, a silicon carbide,a silicon nitride and a solid solution thereof on said surface of saiddiamond sintered body; and after said forming step, processing saiddiamond sintered body to obtain a diamond sintered body tool.
 35. Themethod of manufacturing a diamond sintered body tool according to claim34, wherein said acid solution includes at least one selected from thegroup of nitric acid, hydrochloric acid and hydrofluoric acid.
 36. Themethod of manufacturing a diamond sintered body tool according to claim34, wherein the content of said iron group metal in said surface portionis at most 2.0% by weight.